The present invention relates to a locking method for forcibly halting operation of a work machine and a locking device used for such a method.
FIG. 4 shows a hydraulic shovel as a work machine. The hydraulic shovel has a lower structure 13 including a pair of crawler belts 12 that are disposed at the two lateral sides of the lower structure 13 and driven by a pair of laterally arranged travel motors 11 respectively. An upper structure 16 is attached to the lower structure 13 with a rotating portion 15 therebetween. The rotating portion 15 is so designed as to be driven by a swing motor 14. A cab 17, in which a driving seat for an operator is installed, and a front attachment 18 for performing excavation are mounted on the upper structure 16.
The front attachment 18 includes a boom 20, a stick 22 and an attachment 29, which may be a bucket 24, a breaker or the like. The boom 20 is supported by the upper structure 16 by means of a pin 19, which attaches the boom 20 to a shaft of the upper structure 16 so that the boom 20 is capable of rotating around the shaft. A pin 21 attaches the stick 22 to a shaft disposed at the end of the boom 20 so that the stick 22 is rotatably supported by the boom 20. A pin 23 attaches the attachment 29 to a shaft disposed at the end of the stick 22 so that the attachment 29 is rotatably supported by the stick 22. The boom 20 and the stick 22 are adapted to be rotated by a boom cylinder 25 and a stick cylinder 26 respectively, while the bucket 24 or the attachment 29 is adapted to be rotated by a bucket cylinder 27 and a link mechanism 28.
A work machine having a structure described above is provided with a hydraulic system locking mechanism for locking the supply of oil pressure to various hydraulic actuators, such as the laterally arranged travel motors 11, the swing motor 14, the boom cylinder 25, the stick cylinder 26 and the bucket cylinder 27.
A conventional hydraulic system locking mechanism is directly operated by turning on or off a lock operation switch. Therefore, when an operator releases the hydraulic system from the locked state, the hydraulic system is unlocked regardless of the condition of the machine. In other words, should the hydraulic system lock be released in a situation where signals have been input to one or a number of the operation levers, the work machine suddenly starts running in response to the signals input to the operation lever(s).
In case the lock of the hydraulic system is released when an operation lever is in an unusual, unexpected state, such that, for example, a part of the clothes of the operator is caught by the operation lever, the work machine will move in a way the operator is not aware of. Such an event is not desirable. One of the worst possible cases will be a situation where a worker is near the work machine while signals to command swinging have been input to the operation levers. In such a case, it is absolutely imperative to prevent releasing of the lock of the hydraulic system.
As described above, a work machine equipped with an electronically controlled hydraulic system that functions according to a conventional method is not always safe, because, depending on an outstanding command input to the corresponding operation lever, releasing the lock of the hydraulic system by the operator may undesirably actuate a hydraulic actuator.
In order to solve the above problem, an object of the present invention is to ensure the safety of a work machine by requiring the operator to check the safety before releasing the work machine from the locked state.
Once a work machine becomes locked so that its operation is forcibly halted, a work machine locking method according to the present invention maintains the work machine locked until a safety check is performed.
Therefore, once the work machine becomes locked, even if release of the lock of the work machine is commanded thereafter, the work machine is kept locked and cannot be released from the locked state regardless of whether the operator of the work machine operates the work machine. The locking continues until the operator of the work machine performs a safety check. The invention thus prevents an accident that may otherwise be caused by inadvertent actuation of the work machine due to carelessness of the operator.
Furthermore, in case unlocking of the work machine is commanded in the situation where there is an outstanding actuation command input to the work machine, the aforementioned method calls for maintaining the work machine locked until a safety check is performed.
Therefore, when the work machine is in the state where an actuation command has been input, even if the operator commands unlocking, the work machine is prevented from being actuated until a safety check is performed. The invention thus prevents an accident that may otherwise be caused by the operator""s careless operation to actuate the work machine or release the lock of the work machine.
In case there is an outstanding command for unlocking of the work machine while there is no outstanding actuation command input to the work machine, the aforementioned method calls for maintaining the work machine locked.
When there is no outstanding actuation command input to the work machine, it is often impossible to judge whether the work machine is locked or unlocked. Therefore, even if there is no outstanding actuation command input to the work machine, the invention ensures complete safety by maintaining the work machine locked and calling attention of the operator when unlocking of the work machine has been commanded.
In the method described above, the work machine can be released from the locked state by commanding locking in the state where there is no outstanding actuation command input to the work machine and, thereafter, commanding release of the lock of the work machine.
According to the above method, the work machine is released from the locked state and made ready to be actuated by commanding locking so as to perform a safety check in the state where there is no outstanding actuation command input to the work machine and, thereafter, commanding release of the lock of the work machine. Thus, the invention facilitates a safety check operation.
A work machine locking device according to the present invention includes operating devices for inputting actuation commands to a work machine, a lock commanding means adapted to command locking for halting the work machine or unlocking for enabling the work machine to resume working, an electronic circuit adapted to compute the method of locking said work machine based on signals that have been input from the operating devices and the lock commanding means, and a lock executing means adapted to be controlled by signals output from said electronic circuit so as to maintain or release the work machine at or from the locked state.
As described above, the lock executing means is controlled by signals that have been output from said electronic circuit based on signals input from the operating devices and the lock commanding means. Therefore, locking and unlocking of the work machine can easily be controlled according to signals input from the operating devices and the lock commanding means. For example, in case the operator commands to release the work machine from the locked state in the situation where there is an outstanding actuation command from an operating device, the work machine is maintained locked by the lock executing means, which is controlled based on arithmetic signals from the electronic circuit. In case there is no actuation command from the operating devices, the lock commanding means commands locking and then commands unlocking so that the lock by the lock executing means is released, thereby enabling the actuation of the work machine.
According to another feature of the invention, the aforementioned lock executing means is an electromagnetic selector valve intended for locking the hydraulic system and disposed in a pilot oil feeding line that is adapted to feed pilot pressure to a control valve in a hydraulic circuit, which is adapted to control operation of the work machine. Said electromagnetic selector valve is hereinafter called a hydraulic system locking electromagnetic selector valve.
As described above, the lock executing means consists of a hydraulic system locking electromagnetic selector valve disposed in a pilot oil feeding line that is adapted to feed pilot pressure to a control valve in a hydraulic circuit. Therefore, by controlling the pilot oil pressure by means of the hydraulic system locking electromagnetic selector valve so as to lock the control valve at the neutral position, the work machine can be locked easily and reliably. For example, even if the operator commands to release the work machine from the locked state in the situation where there is an outstanding actuation command from an operating device, the electronic circuit closes the pilot oil feeding line by using the hydraulic system locking electromagnetic selector valve so as to maintain the control valve at the neutral position and, consequently, maintains the work machine at the locked state. In case unlocking of the work machine is commanded after a locking command is sent by the lock commanding means when there is no actuation command from the operating devices, the electronic circuit opens the pilot oil feeding line by opening the hydraulic system locking electromagnetic selector valve so that the control valve is controlled by the pilot oil pressure.